Yikes! Scenario 1 sounds awful!
This doesn't explain how fast the watch is running. It only explains that your mother has her watch set 5mins ahead of your computer.
Does it gain 5mins per day, so after a week it is an hour ahead? Or, has it gained this 5mins since she bought it 4 years ago? Because there is a big difference between these two scenarios.
I recommend automatic watches should be serviced every 5 years, worn daily or not, as the gaskets can dry and crack and the oils can become sticky.